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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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MILES AND GRINNELL GLACIERS                           43S
In 1912 Corser l thought that it had advanced very slightly. We infer from this that the period of activity and advance which began in the fall of 1908 or the spring of 1909 was nearly or quite over in 1911.
Contrast with Advance of Childs Glacier. The advance of Miles Glacier in 1909 and 1910 was without spectacular features. There is little current in the portion of the lake near the ice cliff. The iceberg waves attack the ice cliff little, and melting by the lake waters, though undercutting the ice cliff as salt water does, has not undermined the cliff of Miles Glacier as rapidly as the Copper River mechanically undercuts the Childs Glacier. The infrequency of iceberg falls, and the great distance for the sound to carry, cause persons who traverse the Copper River railway to pay little attention to Miles Glacier, especially as the waves from it nearly disappear before they strike the shore near the railway bridge. This is why the pronounced advance of Miles Glacier in 1909 and 1910 attracted little attention on the part of the thousands of men who were along the line of the railway and the scores who were living near the railway bridge in these years.
The rates of movement during the advance of Miles Glacier were not measured. If it took the whole two years (from 1908 to 1910) for the ice front to move forward the
CHILC&
FIG. 66.   DIAGRAMMATIC SKETCH SHOWING RELATIONSHIPS OF MILES AND CHILDB GLACIERS TO THE RAILWAY
BRIDGE.                                                                       *
The black dots in the horizontal line show positions of the ice cliffs in the years indicated, the advance and retreat between dates being indicated by the arrows below.
measured 4000 feet, the rate of motion was less than 6 feet a day, plus, of course, what was lost through iceberg discharge. From June to August, 1910, it was less than 2 feet a day. In any event it is clear that the recent advance of Miles Glacier was of a mild sort, compared with the rapid and far more spasmodic advance of Childs Glacier in 1910.
We have represented by a diagram (Fig. 66) the relative distances from Miles and Childs Glaciers to the railway bridge at several times in their recent history, selecting the bridge as the point of measurement, because it furnishes a convenient common point. It is clear that if the advance of the great Miles Glacier in 1909 and 1910 had been of the same order of magnitude as that of the smaller Childs Glacier in the latter year, the Miles ice front would easily have gone out to or beyond the railway. That such an event is possible is evident from the advance between 1885 and 1888, which took the ice cliff to within 400 feet of the site of the present bridge.
That this structure could not be placed better in its relation to both Miles and Childs Glaciers, is clearly indicated by the advances of 1888 and 1910. The facts suggest also that a possible great future advance of Miles Glacier would probably be short-lived. If the ice expanded again to the southern terminal moraine, the glacial streams might tear out or bury the railway grade for long stretches south of the bridge, but the deep lake basin and the present channel should soon dispose of most of the water, as they did at the last expansion. Besides possible destruction of the bridge during an advance,
> Corser, Caleb, Personal communication, September SO, 1912. 28